1. Technical Field
This invention relates to an improved rope clamp and, more particularly, to a rope clamp for a terminating end of a high tensile modulus textile rope such as one comprised of multi-strand plastic fibers. Preferably the textile rope is formed of one or more sheaths of fibrous plastic material such as aramid fibers constituting a lightweight line capable of carrying extremely heavy loads. Such rope is widely used by rescue workers, fireman and in various safety and emergency applications. The rope is also frequently used in certain military and marine applications, the rope being resistant to severing, chemicals, shock and the like, it being particularly valuable for aircraft and marine applications due to its great strength and lightweightness.
2. Background Information
Previously, composite ropes fabricated of both metallic and plastic materials into multi-layered flexible lines have been well-known for use in survival-type situations as well as in mountaineering and other hazardous conditions. Such composite ropes are normally formed having a metallic core and one or more outer sheaths of fibrous plastic material. The nylon, polyester or other synthetic material used in the manufacture of such ropes may melt or burn or may be so severely weakened that the rope becomes unsafe for further use. Such composite ropes having a metallic core are not easily assembled around stable terminating fixtures and require an improved terminating end clamp to join the rope to a suitable fitting such as a clevis, yoke or other rope terminating member. U.S. Pat. No. 1,855,227 to Fliege discloses a single wedging plug employed in an inner-conical recess of a sleeve member to clamp a metallic cable to a clevis or turnbuckle. Also co-pending U.S. patent applications entitled "End Clamp for Textile Rope with a Metallic Core", Ser. No. 07/518,572, filed May 3, 1990, now U.S. Pat. No. 5,022,780, issued Jun. 11, 1991, and co-pending application, entitled "End Clamp for Composite Rope", Ser. No. 07/603,315, filed Oct. 25, 1990, U.S. Pat. No. 5,136,755, issued Aug. 11, 1992, are pertinent to the present application, both applications relating to end clamps for composite ropes having a metallic core and outer plastic sheaths. These applications are owned by the same common assignee as the present application.
While composite plastic ropes having a metallic core are particularly desirable for certain applications which utilize the best properties of the outer plastic sheath and the metallic core, there are other applications for all plastic ropes which are formed of multi-strand fibrous materials such as aramid fibers to provide lightweight and great strength for numerous applications. End clamps for such fibrous plastic materials are needed to securely retain the end of such ropes with great durability and stability for their attachment to permanent fixtures and structures.
Aramid fibers are particularly valuable for forming high tensile modulus plastic ropes. Two types of aramid fibers are primarily used for forming such ropes, the first being comprised of heat-resistant fibers, such as Nomex and Conex, and ultra high-strength high-modulus fibers, such as Kevlar and Arenka. Such fibers are relatively expensive compared to other synthetic fibers such as nylon and polyester, however, aramid fibers have particularly unique physical properties which make them highly desirable for forming plastic ropes. The aramid fibers provide improved heat resistance, flame resistance, and dimensional stability which are useful in reinforcing fire hose and V-belts. Also, ultra high-strength, high tensile modulus aramid fibers are used as the tire cord in tire carcasses and as the belt in bias-belted and radial-belted tires, V-belts, cables, parachutes, body armour, and the like.
Aromatic polyamides are formed by reactions that lead to the formation of amide linkages between aromatic rings. In practice, the aramid fibers are formed by the reaction of aromatic diamines and aromatic diacid chlorides in an amide solvent. From solutions of these polymers it is possible to produce fibers of exceptional heat and flame resistance and fibers having excellent to remarkable tensile strength and modulus. Due to the physical property differences between fibers of aromatic and aliphatic polyamides being greater than those between other existing generic classes of fibers, a new generic term for fibers from aromatic polyamides was adopted. The generic term "aramid" was adopted in 1974 by the U.S. Federal Trade Commission for fibers of the aromatic polyamide type. Aramid is a manufactured synthetic fiber in which the fiber-forming is a long chain synthetic polyamide in which 80% of the amide (--CO--NH--) linkages are attached directly to aromatic rings. Aramid fibers and their properties are further defined in Volume 3 of the 24 Volume Series entitled "Encyclopedia of Chemical Technology", pages 213-240, describing the chemical and physical properties and commercial products formed from aramid fibers.
Three other types of such a high tensile modulus textile rope are sold under the trademarks, TWARON, TECHNORA and VECTRAN and are formed of aramid fibers and fibers very similar thereto. These rope of a high tensile modulus of 9.times.10.sup.6 psi and above as compared to other types of synthetic fiber ropes which may have a tensile modulus approaching 2.times.10.sup.6 psi.
It is known that exposure to chemicals can cause the degradation of ropes formed of synthetic plastic materials and ultimately cause their failure. Ropes which have been subjected to such exposure are frequently discarded and not used further as a precautionary measure if subjected to one or more of a wide variety of chemicals. This may be true where chemicals are found on the ground where the rope has been lying and been exposed to such chemicals. The subject aramid fibers for forming the plastic rope of the present invention and its end terminating clamp are exceptionally resistant to a wide variety of chemicals without degradation or loss of strength.
Many known types of composite ropes or cables are difficult to terminate or otherwise manipulate due to their elastic and unwieldy nature. In most cases, a durable secure termination cannot be regularly made with the plastic rope which will cinch tightly enough to hold and provide safe connection of the line for extremely heavy loads and it is normally difficult to increase the diameter of the rope by doubling it to facilitate grasping of the rope. Various types of mechanical terminations of the rope at its end to interconnect with various types of metallic fittings have not been particularly satisfactory, especially where the lines are utilized for heavy loads, commensurate with their full load-carrying capability. The aforesaid aramid or high tensile modulus fibers are capable of forming plastic ropes having significant dimensional stability where a permanent end clamp is highly desirable.